The present invention relates to a vehicle occupant protection apparatus. In particular, the present invention relates to an air bag that is inflatable to two different volumes and that has a vent for discharging inflation fluid.
A known air bag inflates to a first volume and then, upon rupturing of a tear seam or a rupturable stitching section, inflates further to a larger volume. It is known to provide such an air bag with a vent for discharging inflation fluid when the device is inflated to the larger volume. The vent opens, or is uncovered, when the air bag inflates from the partially inflated condition to the fully inflated condition.
If the vent is closed off by a stitching section that is unevenly stressed, then a portion only of the stitching section might open, without the remainder of the stitching section being opened. The vent opening might remain partially covered or closed, and the air bag might not vent inflation fluid in the desired manner.
The present invention is an inflatable vehicle occupant protection device for helping to protect an occupant of a vehicle. The device is inflatable from a deflated condition through a partially inflated condition to a fully inflated condition by inflation fluid from an inflation fluid source. The device comprises flexible material defining an inflation fluid volume for receiving inflation fluid, including a first panel portion on which is located a set of first points and a second panel portion on which is located a set of second points.
A rupturable stitching section holds the set of first points closely adjacent the set of second points when the device is in the deflated condition and when the device is in the partially inflated condition. The rupturable stitching section is rupturable in response to the application of a force greater than a predetermined force in response to inflation of the protection device. Rupturing of the stitching section enables movement of the first panel portion away from the second panel portion, thereby enabling movement of the device from the partially inflated condition to the fully inflated condition. All of the first points on the first panel portion move away from all of the second points on the second panel portion when the rupturable stitching section ruptures and the device moves from the partially inflated condition to the fully inflated condition.
The device includes a vent in the material for discharging inflation fluid from the device. The vent is blocked from fluid flow through the vent when the rupturable stitching section is not ruptured and the device is in the partially inflated condition. The vent opens to an open condition to permit flow of pressurized fluid from the device through the vent in response to rupturing of the rupturable stitching section and movement of the device from the partially inflated condition to the fully inflated condition.